Use a pool to manage the paragraphs.

Author: Yuncong Zhang

Runtime/painting/text_painter.cs

@@ -34,6 +34,10 @@ public TextPainter(TextSpan text = null,
             this._ellipsis = ellipsis;
         }
 
+        public void releaseParagraph() {
+            Paragraph.release(ref this._paragraph);
+        }
+
 
         public float textScaleFactor {
             get { return this._textScaleFactor; }
@@ -43,9 +47,9 @@ public float textScaleFactor {
                 }
 
                 this._textScaleFactor = value;
-                this._paragraph = null;
                 this._layoutTemplate = null;
                 this._needsLayout = true;
+                Paragraph.release(ref this._paragraph);
             }
         }
 
@@ -57,7 +61,7 @@ public string ellipsis {
                 }
 
                 this._ellipsis = value;
-                this._paragraph = null;
+                Paragraph.release(ref this._paragraph);
                 this._needsLayout = true;
             }
         }
@@ -74,7 +78,7 @@ public TextSpan text {
                 }
 
                 this._text = value;
-                this._paragraph = null;
+                Paragraph.release(ref this._paragraph);
                 this._needsLayout = true;
             }
         }
@@ -94,7 +98,7 @@ public TextDirection? textDirection {
                 }
 
                 this._textDirection = value;
-                this._paragraph = null;
+                Paragraph.release(ref this._paragraph);
                 this._layoutTemplate = null;
                 this._needsLayout = true;
             }
@@ -108,7 +112,7 @@ public TextAlign textAlign {
                 }
 
                 this._textAlign = value;
-                this._paragraph = null;
+                Paragraph.release(ref this._paragraph);
                 this._needsLayout = true;
             }
         }
@@ -128,7 +132,7 @@ public int? maxLines {
                 }
 
                 this._maxLines = value;
-                this._paragraph = null;
+                Paragraph.release(ref this._paragraph);
                 this._needsLayout = true;
             }
         }

Runtime/rendering/paragraph.cs

@@ -327,6 +327,8 @@ public override void detach() {
             if (this._hoverAnnotation != null) {
                 RendererBinding.instance.mouseTracker.detachAnnotation(this._hoverAnnotation);
             }
+
+            this._textPainter?.releaseParagraph();
         }
 
         TextSelection _selection;

Runtime/ui/txt/paragraph.cs

@@ -243,6 +243,25 @@ public float ideographicBaseline {
         public bool didExceedMaxLines {
             get { return this._didExceedMaxLines; }
         }
+        
+        static List<Paragraph> _paragraphs = new List<Paragraph>();
+
+        public static Paragraph create() {
+            if (_paragraphs.isEmpty()) {
+                return new Paragraph();
+            }
+
+            Paragraph ret = _paragraphs.last();
+            _paragraphs.RemoveAt(_paragraphs.Count-1);
+            return ret;
+        }
+
+        public static void release(ref Paragraph paragraph) {
+            if (paragraph != null) {
+                _paragraphs.Add(paragraph);
+                paragraph = null;
+            }
+        }
 
         public void paint(Canvas canvas, Offset offset) {
             for (int i = 0; i < this._paintRecordsCount; i++) {

Runtime/ui/txt/paragraph_builder.cs

@@ -15,7 +15,7 @@ public ParagraphBuilder(ParagraphStyle style) {
 
         public Paragraph build() {
             this._runs.endRunIfNeeded(this._text.Length);
-            var paragraph = new Paragraph();
+            var paragraph = Paragraph.create();
             paragraph.setText(this._text.ToString(), this._runs);
             paragraph.setParagraphStyle(this._paragraphStyle);
             return paragraph;